From the viewpoint of simple and inexpensive image production, inkjet recording has been used in a variety of printing fields. As the inkjet recording method, there is an UV-curable inkjet method wherein droplets of inkjet ink are landed on a recording medium and then cured by irradiation with ultraviolet rays to form an image. Recently, the UV-curable inkjet method has been attracting attention for its capability of forming images having high rubfastness and adhesiveness even on recording media which lack ink absorbing properties.
However, the image forming methods using the conventional UV-curable inkjet systems have the drawback of poor image quality due to failure to prevent combining of neighboring dots during high-speed recording such as single pass recording using a line recording head or high speed serial recording. As one of methods for preventing combining of neighboring dots, there has been proposed a technique of adding a gelling agent to a UV-curable inkjet ink (see, for example, PTL 1 and PTL 2).
In order to enhance the durability of printed images formed by various printers, there has been proposed a technique of applying an overcoat composition containing a gelling agent to the printed images (PTL 3).
In order to improve the rub resistance of printed images and to prevent set-off between printed articles stacked atop each other, there has also been proposed a technique applying a clear ink capable of sol-gel phase transition to the printed images (PTL 4). In this technique, in order to make uniform the thickness of the clear ink film, a curing step is preceded by a step of heating a recording medium on which the clear ink has been landed, so that the clear ink surface is smoothened.